Systems, methods, and computer readable media for processing and compounding ultrasound images in the presence of motion

ABSTRACT

An ultrasound imaging method and system. The method comprises: for each of a plurality of steer angles, including a reference steer angle, transmitting acoustic energy to a target region at the particular steer angle, receiving acoustic reflections, and converting the acoustic reflections to an image, with the image being associated with the particular steer angle; computing motion information based on the image associated with the reference steer angle; and generating a compounded ultrasound image based on the image associated with each of the plurality of steer angles and based on the motion information.

BACKGROUND 1. Technical Field

The present disclosure relates generally to ultrasound imaging, and moreparticularly to, systems, methods, and computer readable media for theprocessing and compounding of ultrasound images in the presence ofmotion.

2. Discussion of Related Art

An ultrasound system has become a popular diagnostic tool due to a widerange of applications. Specifically, due to its non-invasive andnon-destructive nature, the ultrasound system has been extensively usedin the medical profession. Modern high-performance ultrasound systemsand techniques are commonly used to produce two or three-dimensionalimages of internal features of an object (e.g., human organs).

The ultrasound system generally uses a probe containing a wide bandwidthtransducer to transmit and receive ultrasound signals. When used withthe human body, the ultrasound system forms images of human internaltissue by electrically exciting an acoustic transducer element or anarray of acoustic transducer elements to generate ultrasound signalsthat travel into or through the body. The ultrasound signals produceultrasound echo signals which are reflected from body tissue, whichappear as discontinuities to the propagating ultrasound signals. Variousultrasound echo signals return to the transducer element and areconverted into electrical signals, which are amplified and processed toproduce ultrasound data for an image of the tissue.

The ultrasound system employs an ultrasound probe containing atransducer array for transmission and reception of ultrasound signals.The ultrasound system forms ultrasound images based on the receivedultrasound signals. The technique of transmitting the ultrasound signalsby steering the ultrasound beam at various angles has been used toobtain ultrasound images having more perspectives of a target region ofinterest.

Additionally, an ultrasound imaging system may include an ultrasoundimaging unit and an image processing unit. The ultrasound imaging unitmay control the transmission of ultrasound signals to a target region,such as tissue, and form data based on echo signals resulting from thetransmitted ultrasound signals. The transmission of ultrasound signalsat various steer angles may also be controlled by the ultrasound imagingunit. Using the echo signals, the ultrasound imaging unit and an imageprocessing unit may generate a composite image of the target region, bycombining the echoes at different steer angles using a technique knownas spatial compounding. In some instances, the target region may moveduring the ultrasound procedure, adversely affecting the echo signals ofone or more steer angles and causing deterioration in the compoundedimage of a target region. Accordingly, there is a need for systems andmethods for determining motion of target regions during an ultrasoundprocedure and applying systems and methods for motion compensation forthe compounded image of a target region.

SUMMARY

The present disclosure is directed to processing and compounding ofultrasound images in the presence of motion. In one aspect, anultrasound imaging method operates, for each of a number of steerangles, including a reference steer angle (RSA), to transmit acousticenergy to a target region at a particular steer angle, receive acousticreflections, and convert the acoustic reflections to an image, with theimage being associated with the particular steer angle. The ultrasoundimaging method computes motion information based on the image associatedwith the reference steer angle and generates a compounded ultrasoundimage based on the image associated with each of the steer angles andbased on the motion information.

In one embodiment, generating the compounded ultrasound image includes,for each of the steer angles, applying a particular weighting to theimage associated with the particular steer angle to generate a weightedimage associated with the particular steer angle, where the particularweighting is based on the motion information, and combining the weightedimages associated with the steer angles to generate the compoundedultrasound image.

In a further embodiment, the image associated with each steer angle hasan H by W array of pixels, where H is a height of the image in number ofpixels and W is a width of the image in number of pixels, and where eachpixel has a pixel value. In one embodiment, computing the motioninformation includes computing a difference between a preexisting imageand the image associated with the reference steer angle (RSA) togenerate a difference image, and filtering the difference image using alow pass filter to generate a filtered difference image having pixelsDis(i,j).

In one aspect, the disclosed ultrasound imaging method operates, foreach of the steer angles other than the reference steer angle, tocompute a weight for each pixel of the image associated with theparticular steer angle, where the steer angles include a number N ofsteer angles designated as 1≤k≤N, and where the weight for each pixel(i,j) of the image associated the particular steer angle k is computedby:

W _(k,k≠rsa)(i,j)=C _(k,k≠rsa)·ƒ(Dis(i,j)), if Dis(i,j)≤TH

W _(k,k≠rsa)(i,j)=0, if Dis(i,j)>TH

where:

ƒ is a function that inverts pixel values such that ƒ(Dis(i,j)) issmaller as Dis(i,j) is larger,

C_(k) are predetermined values where C_(k) is smaller as the steer angleis larger and where Σ_(k=1) ^(N)C_(k)=1, and

TH is a predetermined threshold value.

In yet another embodiment, generating the compounded ultrasound imageincludes computing, for each pixel (i,j):

${{Compounded}\mspace{14mu} {image}\mspace{11mu} \left( {i,j} \right)} = {\sum\limits_{k = 1}^{N}{{W_{k}\left( {i,j} \right)} \cdot {{Image}_{k}\left( {i,j} \right)}}}$

where Image_(k) is the image associated with steer angle k, and where:

W _(k,k=rsa)(i,j)=1−Σ_(k=1,k≠rsa) ^(N) W _(k)(j,k), if Dis(i,j)≤TH

W _(k,k=rsa)(i,j)=1, if Dis(i,j)>TH.

In another embodiment, the reference steer angle is zero degrees, whichis the steer angle corresponding to transmitting acoustic energy fromall transducer elements at the same time. In one embodiment, the motioninformation is computed based further on a previously compoundedultrasound image.

In accordance with at least one aspect of the disclosure, the ultrasoundsystem includes a transducer configured to, for each of a number ofsteer angles, including a reference steer angle, transmit acousticenergy to a target region at a particular of steer angle, receiveacoustic reflections, and convert the acoustic reflections to RadioFrequency (RF) data. The ultrasound system further includes front-endcircuitry configured, for each of the steer angles, to process the RFdata associated with the particular steer angle to generate an imageassociated with the particular steer angle, and a computing deviceconfigured to generate motion information based on the image associatedwith the reference steer angle and generate a compounded ultrasoundimage based on the motion information and the image associated with eachof the steer angles.

In still a further embodiment of the ultrasound system, generating thecompounded ultrasound image includes applying, for each of the steerangles, a particular weighting to the image associated with theparticular steer angle to generate a weighted image associated with theparticular steer angle, where the particular weighting is based on themotion information, and combining the weighted images associated withthe steer angles to generate the compounded ultrasound image.

In another embodiment of the ultrasound system, the image associatedwith each particular steer angle has an H by W array of pixels, where His a height of the image in number of pixels and W is a width of theimage in number of pixels, and where each pixel has a pixel value. Inone embodiment, generating the motion information includes computing adifference between a preexisting image and the image associated with thereference steer angle (RSA) to generate a difference image, andfiltering the difference image using a low pass filter to generate afiltered difference image having pixels Dis(i,j).

In one aspect of the ultrasound system, the computing device is furtherconfigured, for each of the steer angles other than the RSA, to computea weight for each pixel of the image associated with the particularsteer angle, where the steer angles include a number N of steer anglesdesignated as 1≤k≤N, and where the weight for each pixel (i,j) of theimage associated the particular steer angle k is computed by:

W _(k,k≠rsa)(i,j)=C _(k,k≠rsa)·ƒ(Dis(i,j)), if Dis(i,j)≤TH

W _(k,k≠rsa)(i,j)=0, if Dis(i,j)>TH

where:

ƒ is a function that inverts pixel values such that ƒ(Dis(i,j)) issmaller as Dis(i,j) is larger,

C_(k) are predetermined values where C_(k) is smaller as the steer angleis larger and where Σ_(k=1) ^(N)C_(k)=1, and

TH is a predetermined threshold value.

In still a further embodiment of the ultrasound system, generating thecompounded ultrasound image includes computing, for each pixel (i,j):

${{Compounded}\mspace{14mu} {image}\mspace{11mu} \left( {i,j} \right)} = {\sum\limits_{k = 1}^{N}{{W_{k}\left( {i,j} \right)} \cdot {{Image}_{k}\left( {i,j} \right)}}}$

where Image_(k) is the image associated with steer angle k, and where:

$\quad\begin{matrix}{{{W_{k,{k = {rsa}}}\left( {i,j} \right)} = {1 - {\sum\limits_{{k = 1},{k \neq {rsa}}}^{N}{W_{k}\left( {i,j} \right)}}}},} & {{{if}\mspace{14mu} {{Dis}\left( {i,j} \right)}} \leq {TH}} \\{{{W_{k,{k = {rsa}}}\left( {i,j} \right)} = 1},} & {{{if}\mspace{14mu} {{Dis}\left( {i,j} \right)}} > {TH}}\end{matrix}$

In one embodiment of the ultrasound system, the reference steer angle iszero degrees, which is the steer angle corresponding to transmittingacoustic energy from all transducer elements at the same time. In oneembodiment, the motion information is computed based further on apreviously compounded ultrasound image.

The Summary is provided to introduce the present disclosure in acondensed form. This Summary does not relate to key or essentialfeatures and does not define or limit the scope of the presentdisclosure in any way.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the present disclosure are described herein belowwith reference to the drawings, which are incorporated in and constitutea part of this specification, wherein:

FIG. 1 illustrates a top level architecture of one embodiment of anultrasound imaging system, in accordance with aspects of the presentdisclosure;

FIG. 2 illustrates one embodiment of an imaging system of an ultrasoundimaging system, in accordance with aspects of the present disclosure;

FIG. 3 illustrates a block diagram of one embodiment of the operationsof a beamforming unit, in accordance with aspects of the presentdisclosure;

FIG. 4 illustrates a flow diagram of one embodiment of a spatialcompounding method, in accordance with aspects of the presentdisclosure; and

FIG. 5 illustrates the spatial compounding method of FIG. 4, as appliedto a plurality of ultrasound images, in accordance with aspects of thepresent disclosure.

DETAILED DESCRIPTION

The present disclosure relates to performing spatial compounding usingmotion information to reduce blurring. Spatial compounding is anultrasound imaging technique that obtains images of a target region bydirecting ultrasound wave to a target region at different angles, andthen combining the images resulting from each angle. Spatial compoundingcan produce an image with better quality than imaging a target region atonly one angle. Difficulties arise in spatial compounding, however, whena target region is susceptible to motion, such as when imaging a heart,lungs, or a fetus. In such cases, spatial compound can result in imageswith excessive blurring.

An ultrasound probe is an electronic, reusable device having an array oftransducer elements capable of precise waveform timing and intricatewaveform shaping and capable of communicating analog or digitized datato an imaging system. By utilizing independent transducer elements aimedat a target region at various angles and processing the informationobtained by the independent transducer elements, the imaging system iscapable of generating plurality of ultrasound images which may becombined to generate a single ultrasound image which can produce animage of the target region with higher quality than a single uncombinedultrasound image. As discussed in further detail below, variousembodiments of an ultrasound imaging system are provided with respect tospatial compounding in the presence of motion.

FIG. 1 illustrates a block diagram of an ultrasound imaging system 100in accordance with an embodiment of the present disclosure. Ultrasoundimaging system 100 includes a transducer unit 110 containing atransducer array 105 including transducer elements 105 a-z, front-endcircuitry 120, a communication interface 130, a computing device 110,and a display 150. Transducer unit 110 is a device that convertsacoustic energy/acoustic waves into electrical signals and convertselectrical signals into acoustic energy/acoustic waves. As used herein,the term “acoustic” includes waves having audible frequencies (i.e.,below 20 kHz) and waves having ultrasonic frequencies (i.e., above 20kHz). The transducer 100 includes an array of transducer elements 105a-z, which transmit the ultrasound waves toward a target region atspecific and/or predetermined angles referred to as “steer angles.”Ultrasound waves propagate omnidirectionally in the absence ofwaveguides. When all of the transducer elements 105 a-z activate at thesame time, the ultrasound waves created by all of the transducerelements 105 propagate away from the transducer elements at the sametime. This is referred to as zero degree steer angle. Each transducerelement 105 a-z, however, can be individually controlled, and byactivating particular transducer elements at different times, thetransducer unit can adjust the steer angle of the ultrasoundtransmission without physically moving the transducer unit. The wavesfrom the earlier activations will have travelled some distance when thewaves from the later activations are first propagated, thereby forming awave front that appears at an angle relative to the transducer unit 110.Thus, the steer angle can be electronically adjusted using transducertiming, without physically moving the transducer unit 110.

The transducer array 105 receives ultrasound waves that are reflected orechoed from the target region, and transducer unit 110 converts thereceived ultrasound waves to electrical signals. Electrical signalsconverted by transducer unit 110 may be in the form of radio frequency(RF) signals. As shown in FIG. 1, transducer unit 110 is interfaced withor coupled to front-end circuitry 120 via communication line “T.” Asused herein, communication lines “T” denote lines that are capable ofcommunicating RF data, image data, or other electrical signals, and thatprovide an interface between the components of ultrasound imaging system100.

Referring now to front-end circuitry 120, front-end circuitry 120includes a receiver (not shown) that receives RF signals from transducerunit 110, a transmitter (not shown) that transmits RF signals totransducer unit 110, and a front end processor 125. Front-end circuitry120 performs specific processing of the RF signals as described below.Front-end processor 125 can utilize specific ultrasound waveforms, beampatterns, receiver filtering techniques, amplification, and demodulationschemes, for imaging. Front-end circuitry 120 also converts digitalsignals to analog signals and vice versa. Front-end circuitry 120interfaces with and is coupled to transducer unit 110 via transmissionline “T” and also interfaces with computing device 140 via transmissionlines “T” and a communication interface 130. Communication interface 130is an interfacing device that allows front-end circuitry 120 tocommunicate with the computing device 140 and may include a UniversalSerial Bus (USB), such as USB 3.0, or other bus interfaces or protocolscapable of interfacing with computers and electronic devices.

In the illustrated embodiment, computing device 140 includes a centralprocessing unit (CPU) 145 and a graphics processing unit (GPU) 147.Central processing unit 145 and GPU 147 provide image processing andpost-processing of information received from the front-end circuitry120, and can control or direct other operations. In some embodiments,computing device 140 may be a personal computer or a laptop or othercomputing device.

In some embodiments, transducer unit 110 and front-end circuitry 120 arecontained within a single device, which interfaces with computing device140 via communication interface 130. In other embodiments, transducerunit 110 and front-end circuitry 120 are contained in separate devices.In one embodiment, the communication interface 130, the computing device140 and/or the display 150 can be contained within one device. Inanother embodiment, the computing device 140 and the display 150 can beseparate devices. Other configurations are contemplated to be within thescope of the present disclosure.

Referring now to FIG. 2, a block diagram of an imaging system 200 whichincludes computing device 140 and a display 150 is illustrated. System200 is utilized to generate compounded images. System 200 communicateswith the transducer unit and/or front end circuitry (FIG. 1, 110, 120)to receive RF/image data and performs processing on the RF/image data togenerate compounded images. Computing device 140 includes CPU 145,First-In First-Out (FIFO) buffer 134, GPU 147, and may include a display150. In other embodiments, display 150 may, for example, be a separatemonitor outside of computing device 140. CPU 145 is capable offunctioning as, at least, a USB host controller 136. GPU 147 is capableof handling operations such as beamforming, envelope detection, imagecompounding, and image post-processing, which are performed bybeamforming unit 141, envelop detection unit 142, compounding unit 143,and image post-processing unit 144, respectively. As used herein, theterm “beamforming” shall refer to receive beamforming, unless usage orcontext indicates that transmit beamforming or another meaning isintended in any particular instance.

CPU 145 controls the USB host controller 136 to receive the RF/imagedata from the transducer unit and/or the front end circuitry. When theRF/image data is received, CPU 145 transmits and writes the RF/imagedata to FIFO buffer 134. The RF/image data in FIFO buffer 134 is nextprocessed by GPU 147 in the order which it was received, such that thefirst RF/image data received is processed first. FIFO buffer 134 iscoupled with CPU 145 and GPU 147. CPU 145 stores each RF/image data inFIFO buffer 134 as long as the FIFO buffer 135 has available memoryspace.

Turning now to GPU 147, beamforming unit 141 performs processing ofRF/image data by delaying certain signals received by particulartransducer elements 105 a-z, to compensate for certain transducerelements being farther away from the target region than other transducerelements, in order to temporally align the signals received by theindividual transducer elements 105 a-z. After the signals of the varioustransducer elements are aligned, beamforming unit 141 combines the datafrom the various transducer elements to generate RF/image data for asingle image, as illustrated in FIG. 3. Envelope detection unit 142 isconfigured to detect the envelope of the signals generated bybeamforming unit 141, thus removing the carrier signal. Envelopedetection unit 142 is used to detect the peaks in the received RF/imagedata, and log compression is used to reduce the dynamic range of thereceived RF/image data. Compounding unit 143 is utilized to analyzewhether there is motion present in the received RF/image data which mayaffect the compounded images, to correct for the motion, and to combinethe images generated by beamforming unit 141. Following the compoundingprocess by compounding unit 143, a compounded ultrasound image isgenerated. Image post-processing unit 144 is configured to automaticallyenhance the generated ultrasound image for a medical professional ortechnician. The medical professional or technical may control the amountthe generated compounded image is post-processed. The resulting imagemay then be displayed on a screen of the display 150.

FIG. 2 is merely exemplary and in various embodiments, the operationsdescribed in connection with FIG. 2 can be handled by otherconfigurations of processor(s), software, programmable logic devices,integrated circuits, ASICs, circuitry, and/or hardware. For example, incertain embodiments, the CPU or a microprocessor or a digital signalprocessor can handle some or all of the operations. In certainembodiments, some or all of the operations can be performed by hardwareor circuitry, such as the beamforming and envelope detection operations.Other configurations not specifically disclosed herein are contemplatedto be within the scope of the disclosed technology.

Referring now to FIG. 3, FIG. 3 illustrates a block diagram 300 of anexample of beamforming, including filtering, time delaying, and summingas RF/image data is processed by beamforming unit 141 of GPU 147. Asshown in FIG. 3, RF/image data 305 represents data produced bytransducer elements 105 a-z and is read from FIFO buffer 134. RF/imagedata 305 is filtered via filters 310 in order to reduce noise, andfilters 310 may be in the form of finite impulse response filters,infinite impulse response filters or median filters, as each isunderstood by those skilled in the art. The filtered data is delayed bytime delay units 315, which generate output data 317 corresponding toRF/image data 305. As described above, beamforming unit 141 usestemporal delays to compensate for certain transducer elements 105 a-zbeing farther away from the target region than other transducer elements105 a-z, in order to temporally align the signals received by theindividual transducer elements 105 a-z. For example, as ultrasoundreflections are received by transducer unit 110, transducer elements 105a-z closer to the target region will receive the reflections beforetransducer elements 105 a-z that are farther away from the targetregion. Thus, transducer elements 105 a-z will not all receive thereflections at the same time. The temporal delays operate to alignRF/image data 305 from transducer elements 105 a-z in time. After thesignals of transducer elements 105 a-z are aligned, summing unit 320combines all output data 317 and generates beamformed output data 325,for a particular steer angle. Each beamformed output data 325 is aseparate image having a matrix of pixels that is H-pixels high andW-pixels wide, for a particular steer angle.

Referring again to beamforming unit 141 of FIG. 2 and block diagram 300of FIG. 3, beamforming unit 141 may be implemented by a programmablelogic device. The programmable logic device filters, interpolates,demodulates, phases, applies apodization, delays and/or sums thereceived signals, which are operations of beamforming unit 141. Theprogrammable logic device controls the delays and characteristics ofultrasound waveforms, and generates ultrasound waveforms from memory.The programmable logic device may also implement relative delays betweenthe waveforms as well as filter, interpolate, modulate, phase, and applyapodization. The programmable logic device can control beamforming unit141 to perform functions to process the plurality of signals associatedwith multi-element electrically scanned transducer arrays.

Referring now to FIG. 4, a flowchart of one embodiment of a method 400for spatial compounding is illustrated. The flowchart begins at step405, where a plurality of ultrasound images at a plurality of steerangles are formed. As described in the detail descriptions of FIGS. 2and 3, beamforming unit 141 of FIG. 2 is utilized to generate thebeamformed output data 325 of FIG. 3. Each beamformed output data 325 isa different ultrasound image at a different steer angle. There can be anumber N of different steer angles, and one of the steer angles isdesignated as a reference steer angle (RSA). In one embodiment, the RSAcan be the zero degree steer angle. In another embodiment, the RSA canbe a non-zero degree steer angle. The ultrasound images at differentsteer angles include H-by-W matrices of pixels, where H denotes imageheight in number of pixels and W denotes image width in number ofpixels. At step 405, the N ultrasound images at the N different steerangles are formed.

In one embodiment, the method 400 can proceed to step 408 and generate aspatially compounded image without using any motion information, as isknown in the art, and then at step 427, store and display the spatiallycompounded image. In another embodiment, the method 400 can proceed tosteps 410-425 to compute motion information and generate a spatiallycompounded image based on the motion information, as described below.

Step 410 requires a stored preexisting image to be available forpurposes of a difference calculation used to generate information aboutmotion at a target region. The stored, preexisting image serves as abase image where differences from the base image are viewed as beingmotion. If, after step 405, a stored preexisting image is not availablefor the difference calculation, method 400 can proceed to step 408instead. For example, for the first iteration of the spatial compoundingoperation, the method 400 can proceed to step 408. In the seconditeration of the spatial compounding operation where the compoundedimage from the first iteration would be available to serve as a baseimage, the method 400 can proceed to step 410. In the second iteration,the compounded image from the first iteration would be used for thedifference calculation in the second iteration at step 410.

At step 410, a stored image is selected and the ultrasound image withthe RSA is selected, and a difference calculation is performed betweenthe two selected images. In one embodiment, the stored image can be apreexisting, previously compounded image. In one embodiment, the storedimage can be a preexisting ultrasound image associated with a steerangle other than the RSA.

The difference calculation is performed between each pixel coordinate(i,j) of the stored, preexisting image and the corresponding pixelcoordinate (i,j) of the ultrasound image at the reference steer angle,based on equation (1) below, where (i,j) denotes a pixel coordinate andwhere 1≤i≤H and 1≤j≤W.

Difference image(i,j)=|Preexisting image(i,j)−Reference steer angleimage(i,j)|  (1)

At step 415, preprocessing is performed on the difference image. In oneembodiment, the difference image computed based on equation (1) above isfiltered. The resulting filtered difference image is denoted as Dis, andeach pixel therein is denoted as Dis(i,j). In one embodiment, the filtercan be a low pass filter that reduces noise in the difference image,such as a a 5*5 median filter or a Gaussian smoothing filter. Otherfilters are contemplated to be within the scope of the presentdisclosure. This filtered difference image provides an indication ofmotion of the target region during imaging and serves as motioninformation. In one embodiment, the difference image does not need to befiltered and itself serves as the motion information. The differencecalculation of equation (1) is exemplary. Other ways of determiningmotion information are contemplated to be within the scope of thepresent disclosure.

Next, at step 420, a weight matrix is generated for each ultrasoundimage at each non-rsa based on equations (2)-(7) below:

W _(k,k≠rsa)(i,j)=C _(k,k≠rsa)*ƒ(Dis(i,j))  (2)

where k is the steer angle ID and 1≤k≤N, and where N is the number ofsteer angles, and rsa is the reference steer angle. The coefficientC_(k) is a predetermined coefficient associated with steer angle k. Thefunction ƒ(Dis(i,j)) is a function applied to each pixel coordinate(i,j) of the filtered difference image. C_(k) serves as a steerangle-specific coefficient applicable to every pixel of the imageassociated with steer angle k, and ƒ(Dis(i,j)) serves as apixel-specific weight applicable to pixel coordinate (i,j) in theultrasound images of every steer angle. Thus, equation (2) computes aweight W_(k,k≠rsa)(i,j) for steer angle k and pixel coordinate (i,j)using an angle-specific coefficient and a pixel-specific weight. In oneembodiment, C_(k) becomes larger as the steer angle approaches the RSA:

$\begin{matrix}{P_{k} = {1 - \frac{{k - {rsa}}}{N}}} & (3) \\{C_{k} = {P_{k}/{\sum\limits_{1}^{N}P_{k}}}} & (4) \\{{\sum\limits_{k = 1}^{N}C_{k}} = 1} & (5)\end{matrix}$

Equation (3) generates an intermediate variable P_(k), which decreasesas the steer angle k diverges from the rsa and is largest (equal to 1)when the steer angle is the rsa. Equation (4) generates C_(k) and isused to normalize the values of C_(k) so that the sum of C_(k) acrossall steer angles k is 1, as shown in equation (5). In other words, asthe steer angle diverges from the RSA, the weight given to each pixelcoordinate (i,j) at that specific steer angle is decreased.

In one embodiment, ƒ(Dis(i,j)) has an inverse relationship withDis(i,j), such that ƒ(Dis(i,j)) decreases in value as Dis(i,j) increasesin value. In this manner, W_(k,k≠rsa)(i,j) generally decreases in valueas Dis(i,j) increases in value, for a particular steer angle k. Thus,pixels that reflect greater motion are more lightly weighted for spatialcompounding, and pixels that reflect lesser motion or no motion are moreheavily weighted for spatial compounding.

Next, at step 422, pixel coordinates (i,j) whose motion informationDis(i,j) exceeds a predetermined threshold for Dis(i, j) are excludedfrom the compounding process. Where a pixel coordinate (i,j) has aDis(i,j) value that exceeds the predetermined threshold for Dis(i,j), itis determined that motion of the ultrasound image at or around pixelcoordinate (i,j) exceeds acceptable movement for compounding, andtherefore, compounding the ultrasound image at those pixel coordinates(i,j) would not produce an image of the target region with sufficientquality. An example of such a threshold value (TH) is shown in equation(6):

TH=ƒ ₁(ƒ_(s))  (6)

where f_(s) is the frame rate of the ultrasound imaging system, and ƒ₁is a function that inverts f_(s) such that ƒ₁(ƒ_(s)) is smaller as ƒ_(s)is larger. For example, the threshold value can be TH=a+b/ƒ_(s), where aand b are constants.

In such a situation where a pixel coordinate is excluded from thecompounding process, the weights W_(k,k≠rsa)(i,j) assigned to the pixelcoordinate (i,j) of every non-reference steer angle k is set to the rsa,and the weight W_(k=rsa)(i,j) assigned to the pixel coordinate (i,j) ofthe reference steer angle rsa is set to 1, as shown in equation (7):

$\begin{matrix}{{W_{k,{k \neq {rsa}}}\left( {i,j} \right)} = {{0\mspace{14mu} {and}\mspace{14mu} {W_{rsa}\left( {i,j} \right)}} = {{1 - {\sum\limits_{{k = 1},{k \neq {rsa}}}^{N}{W_{k}\left( {i,j} \right)}}} = 1}}} & (7)\end{matrix}$

The weight metric W_(k)(i,j) at pixel coordinate (i,j) and steer angle kis included in a weight table W_(k), which is utilized during spatialcompounding of step 425. At step 425, spatial compounding is performed,as described in further detail in the description of FIG. 5, and aspatially compounded image is generated and stored in memory. Next, atstep 427, the spatially compounded image is stored and displayed. Theweighting technique of equations (2)-(7) is exemplary. Other weightingapproaches are contemplated to be within the scope of the presentdisclosure.

Next, method 400 proceeds to step 430 and generates a new ultrasoundimage at another steer angle. Next, method 400 returns to step 410 wherethe difference calculation is computed using the previously compoundedimage from step 425, and the motion information is determined at step415. As described in more detail below in the description of FIG. 5,steps 420-425 then operate to generate a new spatially compounded imageusing the motion information determined at step 415 and the newultrasound image previously formed at step 430.

Thus, spatial compounding is performed using all images at various steerangles, but those images which have pixels with higher weights have agreater effect on the final compounded image than those images whichhave pixels with lower weights. Furthermore, in generating the spatiallycompounded image, static portions of images will be compounded with alarger weight than portions of images with motion, thereby decreasingmotion blurring for the final spatially compounded image. The flow ofoperations in FIG. 4 is exemplary and, unless indicated otherwise, theoperations can be performed in a different order and/or can be performedin parallel.

Referring now to FIG. 5, a diagram 500 illustrating the spatialcompounding of step 425 of FIG. 4 is provided. As illustrated in FIG. 5,a plurality of images 505 (I₁-I_(N)) associated with different steerangles 1 through N are shown as a plurality of H-by-W pixel matrices.Motion information and weighting for each of the steer angles arecomputed as described above with respect to steps 410-422 of FIG. 4. Instep 425 of FIG. 4, images 505 (I₁-I_(N)) are weighted and combined toform a spatially compounded image denoted as Res, according to equation(8):

$\begin{matrix}{{{Res}\left( {i,j} \right)} = {\sum\limits_{k = 1}^{N}{{W_{k}\left( {i,j} \right)}*{I_{k}\left( {i,j} \right)}}}} & (8)\end{matrix}$

where Res(i,j) corresponds to pixel coordinate (i,j) in the compoundedimage 520, generated from the spatial compounding of the plurality ofimages 505 (I₁-I_(N)), with each weight table W_(k)(i,j) being appliedto the pixels of corresponding image I_(k). The weight tables W_(k)(i,j)are determined at steps 420-422 in FIG. 4. The spatially compoundedimage Res1 is stored and displayed.

FIG. 5 also illustrates step 430 of FIG. 4, which generates a newultrasound image for another steer angle. As shown in FIG. 5, compoundedimage 520 (Res1) corresponds to a compounding of plurality of images 505(I₁-I_(N)). When a new ultrasound image I_(1′) becomes available (step430 in FIG. 4), it replaces image I₁ and a new compounded image 520(Res2) is generated using the new image I_(1′) by compounding theplurality of images 505 (I₂-I_(N) and I_(1′)) (step 425 of FIG. 4).

The disclosed system sequentially generates ultrasound images at steerangles 1 through N. After the ultrasound image at steer angle N isgenerated, the system cycles back to steer angle 1 and repeats. Eachimage I includes all RF/image data 305 from all of transducer elements105 a-z of transducer array 105, for a particular steer angle.Initially, the first spatially compounded image is generated based onthe images I₁ through I_(N). When the system cycles back to steer angle1 again, a new image I_(1′) replaces the first image I₁. When viewed intime, the “window” for spatial compounding changes from using images I₁through I_(N), to using images I₂ through I_(N) and I_(1′). Personsskilled in the art will recognize this methodology to be what is knownas a “sliding window” technique. In the next iteration, the systemgenerates a new image I_(2′) at steer angle 2, and the new image I_(2′)replaces the first image I₂. Then, when viewed in time, the window forspatial compounding changes from using images I₂ through I_(1′), tousing images I₃ through I_(N) and I_(1′) and I_(2′) (I_(1′) and I_(2′)replace I₁ and I₂, respectively, and therefore for compounding purposesan N number of steer angles is always utilized during compounding).Thus, as the steer angle of transducer unit 110 is changed and sweptthrough angles 1-N, compounding and display operations of imaging system200 continually compounds and updates the display of the compoundedimage by removing a previous image and including one new image of thesame steer angle. In this manner, the initial latency for generating anddisplaying the first spatially compounded image Res1 is N beamformingtime periods, but the latency thereafter for generating and displayinganother spatially compounded image Res2 shortens to one beamforming timeperiod, thereby increasing the display frame rate of the ultrasoundimaging. Based on the aforementioned systems, methods, and devices,spatial compounding of images for a target region that is moving iscompleted with greater clarity through the use of the imaging andultrasound device and methods disclosed and described herein. Thespatial compounding operation of FIG. 5 is exemplary and variations arecontemplated to be within the scope of the present disclosure. Forexample, spatial compounding does not need to be performed every time anew ultrasound image is available. For example, spatial compounding canbe performed for every two new ultrasound images, or at anotherfrequency or interval. Similarly, motion information does not need to begenerated every time a new ultrasound image is available and can begenerated at another frequency or interval.

A computer or computing device may be incorporated within one or moreultrasound imaging system or one or more electronic devices or serversto operate one or more processors to run the ultrasound imaging system.It is to be understood, therefore, that this disclosure is not limitedto the particular forms illustrated and that it is intended in theappended claims to embrace all alternatives, modifications, andvariations which do not depart from the spirit and scope of theembodiments described herein. Detailed embodiments of devices, systemsincorporating such devices, and methods using the same as describedherein. However, these detailed embodiments are merely examples of thedisclosure, which may be embodied in various forms. Therefore, specificstructural and functional details disclosed herein are not to beinterpreted as limiting, but merely as a basis for the claims and as arepresentative basis for allowing one skilled in the art to variouslyemploy the present disclosure in appropriately detailed structure.

The detailed description is provided with reference to the accompanyingdrawings. One of ordinary skill in the art will recognize that thedescription is illustrative only and is not in any way limiting. Otherembodiments of the present disclosure will be understood by personsskilled in the art, having the benefit of this disclosure, as beingwithin the scope of the disclosed technology. While several embodimentsof the disclosure have been shown in the drawings, it is not intendedthat the disclosure be limited thereto, as it is intended that thedisclosure be as broad in scope as the art will allow and that thespecification be read likewise. Therefore, the above description shouldnot be construed as limiting, but merely as exemplifications ofparticular embodiments. Those skilled in the art will envision othermodifications within the scope and spirit of the claims appended hereto.

1. An ultrasound imaging method comprising: for each of a plurality ofsteer angles, including a reference steer angle: transmitting acousticenergy to a target region at a particular steer angle; receivingacoustic reflections; and converting the acoustic reflections to animage, the image being associated with the particular steer angle;computing a motion information based on the image associated with thereference steer angle; and generating a compounded ultrasound imagebased on the image associated with each of the plurality of steer anglesand based on the motion information.
 2. The method according to claim 1,wherein generating the compounded ultrasound image comprises: for eachof the plurality of steer angles, applying a particular weighting to theimage associated with the particular steer angle to generate a weightedimage associated with the particular steer angle, wherein the particularweighting is based on the motion information; and combining the weightedimages associated with the plurality of steer angles to generate thecompounded ultrasound image.
 3. The method according to claim 1, whereinthe image associated with each particular steer angle comprises an H byW array of pixels, wherein H is a height of the image in number ofpixels and W is a width of the image in number of pixels, and whereineach pixel has a pixel value.
 4. The method according to claim 3,wherein computing the motion information comprises: computing adifference between a preexisting image and the image associated with thereference steer angle to generate a difference image, wherein thedifference image comprises, for each pixel coordinate (i,j) where 1≤i≤Hand 1≤j≤W:Difference image(i,j)=|Preexisting image(i,j)−Reference steer angleimage(i,j)|.
 5. The method according to claim 4, wherein computing themotion information further comprises filtering the difference imageusing a low pass filter to generate a filtered difference image havingpixels Dis(i,j).
 6. The method according to claim 5, further comprising:for each of the plurality of steer angles other than the reference steerangle (rsa), computing a weight for each pixel of the image associatedwith the particular steer angle, wherein the plurality of steer anglesinclude a number N of steer angles designated as 1≤k≤N, and wherein theweight for each pixel (i,j) of the image associated the particular steerangle k is computed by:W _(k,k≠rsa)(i,j)=C _(k,k≠rsa)·ƒ(Dis(i,j)), if Dis(i,j)≤THW _(k,k≠rsa)(i,j)=0, if Dis(i,j)>TH wherein: ƒ is a function thatinverts pixel values such that ƒ(Dis(i,j)) is smaller as Dis(i,j) islarger, C_(k) are predetermined values where C_(k) is smaller as thesteer angle is larger and where C_(k=1) ^(N)C_(k)=1, and TH is apredetermined threshold value.
 7. The method according to claim 6,wherein generating the compounded ultrasound image comprise computing,for each pixel (i,j):${{Compounded}\mspace{14mu} {image}\mspace{11mu} \left( {i,j} \right)} = {\sum\limits_{k = 1}^{N}{{W_{k}\left( {i,j} \right)} \cdot {{Image}_{k}\left( {i,j} \right)}}}$wherein Image_(k) is the image associated with steer angle k, andwherein:W _(k,k=rsa)(i,j)=1−Σ_(k=1,k≠rsa) ^(N) W _(k)(i,j), if Dis(i,j)≤THW _(k,k=rsa)(i,j)=1, if Dis(i,j)>TH.
 8. The method according to claim 1,wherein the reference steer angle is zero degrees.
 9. The methodaccording to claim 1, wherein the motion information is based onmovement of the target region.
 10. The method according to claim 1,wherein generating the compounded ultrasound image includes performingenvelope detection, compounding, and post-processing by a graphicsprocessing unit.
 11. The method according to claim 1, wherein the motioninformation is computed based further on a previously compoundedultrasound image.
 12. An ultrasound system comprising : a transducerconfigured to, for each of a plurality of steer angles, including areference steer angle: transmit acoustic energy to a target region at aparticular of steer angle, receive acoustic reflections, and convert theacoustic reflections to Radio Frequency (RF) data; a front-end circuitryconfigured, for each of the plurality of steer angles, to process theradio frequency (RF) data associated with the particular steer angle togenerate an image associated with the particular steer angle; and acomputing device configured to: generate motion information based on theimage associated with the reference steer angle, and generate acompounded ultrasound image based on the motion information and theimage associated with each of the plurality of steer angles.
 13. Thesystem according to claim 12, wherein generate the compounded ultrasoundimage comprises: apply, for each of the plurality of steer angles, aparticular weighting to the image associated with the particular steerangle to generate a weighted image associated with the particular steerangle, wherein the particular weighting is based on the motioninformation; and combine the weighted images associated with theplurality of steer angles to generate the compounded ultrasound image.14. The system according to claim 12, wherein the image associated witheach particular steer angle comprises an H by W array of pixels, whereinH is a height of the image in number of pixels and W is a width of theimage in number of pixels, and wherein each pixel has a pixel value. 15.The system according to claim 14, wherein generate the motioninformation comprises: compute a difference between a preexisting imageand the image associated with the reference steer angle to generate adifference image, wherein the difference image comprises, for each pixelcoordinate (i,j) where 1≤i≤H and 1≤j≤W:Difference image(i,j)=|Preexisting image(i,j)−Reference steer angleimage(i,j)|.
 16. The system according to claim 15, wherein generate themotion information further comprises: filter the difference image usinga low pass filter to generate a filtered difference image having pixelsDis(i,j).
 17. The system according to claim 16, wherein the computingdevice is further configured to compute, for each of the plurality ofsteer angles other than the reference steer angle (rsa), a weight foreach pixel of the image associated with the particular steer angle,wherein the plurality of steer angles include a number N of steer anglesdesignated as 1≤k≤N, and wherein the weight for each pixel (i,j) of theimage associated the particular steer angle k is computed by:W _(k,k≠rsa)(i,j)=C _(k,k≠rsa)·ƒ(Dis(i,j)), if Dis(i,j)≤THW _(k,k≠rsa)(i,j)=0, if Dis(i,j)>TH wherein: ƒ is a function thatinverts pixel values such that ƒ(Dis(i,j)) is smaller as Dis(i,j) islarger, C_(k) are predetermined values where C_(k) is smaller as thesteer angle is larger and where Σ_(k=1) ^(N)C_(k)=1, and TH is apredetermined threshold value.
 18. The system according to claim 17,wherein generating the compounded ultrasound image comprise computing,for each pixel (i,j):${{Compounded}\mspace{14mu} {image}\mspace{11mu} \left( {i,j} \right)} = {\sum\limits_{k = 1}^{N}{{W_{k}\left( {i,j} \right)} \cdot {{Image}_{k}\left( {i,j} \right)}}}$wherein Image_(k) is the image associated with steer angle k, andwherein:W _(k,k=rsa)(i,j)=1−Σ_(k=1,k≠rsa) ^(N) W _(k)(i,j), if Dis(i,j)≤THW _(k,k=rsa)(i,j)=1, if Dis(i,j)>TH.
 19. The system according to claim12, wherein the reference steer angle is zero degrees.
 20. The systemaccording to claim 12, wherein the motion information is based onmovement of the target region.